The present disclosure relates to disc brake assembly having one or more rotating discs having annular friction surfaces thereon against which are forced stationary friction pads for applying a braking force to the rotating discs. In particular, the disclosure relates to disc brakes of the type having the brake friction pads urged into contact with the annular friction surface on the rotor disc by springs for providing the desired braking force break away or starting torque on the disc. This type of disc brake utilizes an annular piston responsive to applied fluid pressure in an annular pressure chamber to move the piston axially to release the piston pads from the annular disc and thereby release the braking force on the disc.
Disc brakes of the aforesaid type are used in heavy machinery applications such as oil well drilling rigs and surface mining equipment; and, in certain applications, may function as an emergency stop brake. One example of brakes of this type employs rotor discs having a diameter of 50 inches (127 cm) and having a break away or startup torque of 5,578,000 in-lbs (630,282 Newton meters).
Referring to FIGS. 6 and 7, the friction pads have heretofore been mounted on a pressure plate 1 secured by spacers 4 and bolts 5 to a housing 2 which forms the annular pressure chamber 3. An annular piston 6 disposed in the chamber 3 has apertures which are slidably positioned over spacers 4. The pressure plate 1 has apertures which are slidably received over spacers 7; and, the piston 6 is secured by a circumferential array of threaded studs 19 and lock nuts 19a over spacers 7 to an annular stationary mounting plate 8 such that fluid pressurization of the cavity results in axial movement of the housing and pressure plate 1. Rotor discs 9, 10 are received over a driving hub 11 and splined thereon to permit axial movement of the disc on spline 10 with respect to the hub 11 while maintaining rotary driving engagement with the hub. A plurality of brake pressure springs 12 are disposed in a circumferential array about the piston 6 with one end of each spring registered against piston 6 and the opposite end of each spring registered against the pressure plate 1. In operation, without fluid pressure in chamber 3, the springs 12 force the pressure plate 1 and housing 2 in a leftward direction in FIGS. 6 and 7 thereby compressing friction pads 14 disposed about the rotor disc 9 against the annular friction surface of the rotor and moves the rotor disc 9 into contact with friction pads 15 mounted on an axially movable annular reaction plate 16, which is slidably movable axially on the spacers 7, but restrained from rotation by the bolts 19 and spacers 7. Reaction plate 16 has friction pads 17 disposed thereabout which are forced against an annular friction surface on a second rotor disc 10 which moves axially against friction pads 18 provided on the pressure plate 1 thereby compressing all of the friction pads against all of the friction surfaces on the rotors and effecting a desired stopping torque.
In operation, when fluid pressure is applied in the chamber 3, the housing 2 moves and moves the pressure plate 1 in a rightward direction, compressing springs 12 against pressure plate 1, thereby releasing pressure on the friction pads 14, 15, 17, 18, movable plate 16, rotor discs 9, 10 and pressure plate 1 for releasing the braking action on rotor discs 9, 10.
The aforesaid prior art brakes have, in service, suffered from cantilevered axial deflection of the radially inwardly region of the pressure plate 1 under the urging of the springs 12 such that the radially inner portion of pressure plate 1 is deflected axially leftward in FIGS. 6 and 7 which results in braking forces localized on the radially inward regions of the rotor discs; and, accordingly, a level of initial stopping torque less than desired is provided with the brake engaged. Accordingly, it has been desired to provide a way or means of eliminating the effects of bending of the reaction components of a disc brake and thereby achieving the desired initial stopping torque for a given design level of force on the friction pads by the springs.